This invention relates to organophosphorus compounds, especially organophosphates and organothiophosphates. More particularly, it relates to the electrochemical synthesis of organophosphates and organothiophosphates in compartmented or uncompartmented cells at ambient temperature and pressure.
Neutral organic esters and thioesters of phosphoric acid have been synthesized in the past by the reaction of phosphorus trichloride and phosphorus oxychloride with alcohols, phenols, mercaptans, or thiophenols. More recently organic phosphates have been prepared by the reaction of phosphorus pentachloride with ethers, as disclosed in U.S. Pat. No. 2,407,279. Employing phosphorus halides to make organic phosphates or thiophosphates generates hydrogen halides as by-products, which are corrosive, difficult to handle, and troublesome to dispose of in an environmentally sound manner. The reaction of phosphorus pentoxide with organic hydroxyl or sulfhydryl compounds requires high temperatures, often high pressure, and the maintenance of supplies of reactive chemicals in inventory.
Warshawsky, Tomilov, and Smirnov published in the All-Union Journal of General Chemistry 7, 598 (1962-USSR) a description of an electrochemical process for the synthesis of trialkyl phosphates by passing current between graphite electrodes in a cell containing alcoholic hydrogen chloride and a suspension of red phosphorus. Trimethyl, triethyl, tributyl and triamyl phosphates were made from the respective alcohols by this procedure.
Fraser in U.S. Pat. No. 2,133,290 of 1938 disclosed a process for making iron oxide and sodium phosphate in an electrolytic cell with a ferrophosphorus anode, a graphitic or lead cathode, and a concentrated aqueous caustic electrolyte.
In U.S. Pat. No. 2,173,103 of 1939 Fraser disclosed a process for making iron phosphate in an electrolytic cell with a ferrophosphorus anode, a graphitic or lead cathode, and a concentrated aqueous solution of an alkali metal salt plus, optionally, alkali metal hydroxide as the electrolyte.
In U.S. Pat. No. 3,730,864 of 1973 Tarjanyi disclosed a process for decreasing the phenolic content of dilute aqueous solutions electrochemically by passing current through a cell packed 40-80% by volume with a bed of particles in the electrolyte. One of the numerous types of particles which Tarjanyi discloses for the electrolytic bed is ferrophosphorus, which is not named as a possible electrode, however.
A principal object of the invention is to produce organophosphorus compounds directly from ferrophosphorus. Another object of the invention is to utilize ferrophosphorus, a by-product of the winning of elemental phosphorus from phosphate rock. Still another object of the invention is to produce trialkyl phosphates and thiophosphates without generating hydrogen chloride as a by-product. A further object of the invention is to produce organophosphorus compounds at ambient temperatures and pressures. Other objects of the invention will be evident to those skilled in the art from study of the description and examples below.